1. Field of the Invention
The present invention is generally related to variable-cycle internal combustion engines, and in particular is concerned with an apparatus to selectively vary intake air flows and pressures, exhaust gas back pressure and flows, and the phase relationship of a pair of crankshafts, thereby selectively varying the timing and compression ratio of a double crankshaft opposed-piston engine to enhance engine efficiency and increase engine power under design and off-design conditions.
2. Description of the Related Art
Generally, many of the cycle operating parameters of an internal combustion engine are fixed at the time of manufacture. These parameters are often set by the fixed geometry of the engine or the timing relationships between various mechanisms, such as valve timing, ignition timing or fuel injection schedules. These relationships and values are often selected to allow reasonably good operation over the engine's full range of power and speed but are never optimum at any of the operating points. Other engines have their relationships selected to favor just one or two narrow operating regimes, but then are seriously deficient at the other operating design points. For example, engine compression ratio and intake/exhaust port timing are generally fixed by the engine's geometry and the actuating assemblies. As the engine operates throughout its entire range, firing temperatures, peak cylinder pressures and scavenging levels may never simultaneously be at their optimum relative levels.
An engine designed for maximum power levels may not operate efficiently at lower speeds. Parameters such as peak cylinder temperatures and pressures at a maximum power level or port scavenging at high operating speeds can result in a compression ratio and port timing that is inefficient and inappropriate at lower power and speed settings.
The Junker engine was developed and used as an aircraft engine in Germany early in the twentieth century. The engines included pairs of opposed pistons mounted in multiple cylinders and controlled by a pair of synchronized gear crankshafts. A detailed description of the Junker engine is found at Chapter X of Aircraft Diesels by Paul H. Wilkinson (Pitman Publishing Corp., NY, NY).
U.S. Pat. No. 2,401,188, which issued to Prince in 1946, shows an internal combustion engine having a variable compression ratio. A pair of sprockets are secured to respective piston drive shafts in an opposed piston internal combustion engine. A loose chain is wrapped around and connects the sprockets. A frame selectively takes up the slack of the top or bottom chain element to vary the phase relationship of the crankshafts to achieve a change in compression ratio.
U.S. Pat. Nos. 4,312,306 and 4,419,969, issued to Bundrick, Jr., show an internal combustion engine having a pair of opposed pistons connected to cranks of unequal throws. The pistons are adjustable in opposing linear travel to define a flexible cylinder head.
Consequently, a need exists for improvements in internal combustion engines. It is desirable that an engine eliminate the restrictions of fixed geometry and consequential inefficient cycle operating parameters as the engine moves through its entire range of operation. It is also desirable for an engine to permit continued adjustment of cycle operating parameters while running for the most efficient operation possible without exceeding mechanical design limits. It is also desirable for the intake and exhaust conditions to be simultaneously controlled so that parasitic power losses are reduced and cylinder air charges are densified as needed. It is also desirable that intake/exhaust power extraction systems be applied effectively and the engine geometry changes be coordinated with intake/exhaust changes.